1. Field of the Invention
The present invention relates to driving force transmission devices that transmit a driving force between rotary members.
2. Description of the Related Art
Conventionally, driving force transmission devices are known in the art which are used for, e.g., driving force transmission systems for vehicles and which are capable of permitting and cutting off transmission of a driving force between rotary members. See, e.g., International Patent Publication No. 2005/106272 WO (2005/106272).
A clutch device described in WO 2005/106272 is used for transmissions for vehicles, and includes: first friction discs that spline engage with the outer peripheral surface of a shaft-like clutch hub; second friction discs that spline engage with a cylindrical clutch drum; an electric motor that generates power pressing the first and second friction discs against each other; and a lock mechanism that maintains the pressing force for the first and second friction discs in the state where current supply to the electric motor is cut off. The power of the electric motor is reduced in speed by a speed reduction mechanism and is converted to linear motion by a cam mechanism to operate the lock mechanism.
The second embodiment (see FIG. 11) of WO 2005/106272 describes that a cylindrical latch mechanism can be used as the lock mechanism. This latch mechanism has: a first inner cylinder having a switch slope; an outer cylinder in which shallow and deep grooves as positioning grooves are alternately arranged in the circumferential direction; and a second inner cylinder having a moving pin. The latch mechanism can switch between a locked state where the moving pin is held in the shallow grooves and an unlocked state where the moving pin is held in the deep grooves, by moving the moving pin of the second inner cylinder between the shallow and deep grooves of the outer cylinder by the switch slope of the first inner cylinder.
Tilted surfaces tilted with respect to the circumferential direction are formed on the axial end faces of the first inner cylinder and the outer cylinder. The moving pin of the second inner cylinder moves between the shallow and deep grooves by sliding on these tilted surfaces. When the moving pin moves into the shallow grooves, the second inner cylinder presses the first and second friction discs against each other. When the moving pin moves into the deep grooves, the second inner cylinder does not press the first and second friction discs against each other.
In the clutch device described in WO 2005/106272, the moving pin of the second inner cylinder slides on the tilted surfaces formed on the axial end faces of the first inner cylinder and the outer cylinder. The second inner cylinder therefore needs to be subjected to a pressing force in the axial direction from a clutch formed by the first friction discs and the second friction discs. If this pressing force is not applied, operation of the lock mechanism may not be reliably performed.